Pulverized fuel burner



Jan. 22, 1963 E. c. HUGE ETAL PULVERIZED FUEL BURNER Filed Sept. 4, 1958 2 Sheets-Sheet 1 FIG. 1

INVENTORS Ernesr C. Huge George Musai ATTORNEY Jan. 22, 1963 E. c. HUGE ETAL PULVERIZEZD FUEL BURNER Filed'Sept. 4, 1958 2 Sheets-Sheet 2 sjwfii $4.12.. 13:23:34.1.

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1m ENTORS Ernesr C. Huge BY George Musar ATTORNEY United states harem 3,974,361 PULVERHZED FUEL BURNER Ernest {1. Huge, Akron, and George Musat, (lantern, Qhio, assignors to The Bahcoclr & Wilcox Company, New York, N.Y., a corporation of New Ziersey Filed Sept. 4, 1958, Ser. No. 758,982 11 Gains. (Cl. flit-23) This invention relates generally to a fuel burner and more particularly to an improved pulverized fuel burner.

It has been observed in pulverized fuel burners that in spinning or whirling a mixture of pulverized fuel and carrier air axially through a burner nozzle, the major portion of the fuel particles tends to concentrate along the inner surface of the nozzle. In doing so the fuel assumes the form of a spiral rope. For this reason the fuel is not uniformly distributed about the entire circumference of the nozzle at its discharge end. Thus, the spiral rope effect results in a major portion of the fuel being discharged over only a relative small segment of the nozzle circumference. This undesirable, heavy, localized fuel, discharge results in certain portions of the furnace receiving too much fuel and too little air while other portions thereof receive, conversely, too little fuel and too much air.

It has been further noted in pulverized fuel burners in which the mixture of fuel and air is whirled axially of a burner nozzle that a relatively low pressure zone is created at the center of the whirling mixture. This low pressure area results in a back-flow of the fuel and air to occur thereat and leads to coking and/or burning within the burner nozzle.

Also in burners of this type secondary air is generally introduced through an air register adjacent the discharge end of the burner nozzle with the register imparting a spin to the secondary air. Because of the spin, a large portion ofthe secondary air is concentrated in only a relatively narrow band which tends to hug the inner periphery of the burner port or throat. For this reason the secondary air is not uniformly distributed over the entire area of the throat opening and consequently mixing of the fuel with the secondary air is not thorough or complete. Be cause of the unequal distribution of the pulverized fuel due to. the spiral rope effect and the incomplete mix ing of the secondary air with the fuel, poor combustion and ineflicient utilization of the fuel is had. This in turn lowers the efiiciency of the furnace or unit fired thereby.

An object of this invention is to provide an improved, pulverized fuel burner in which the spiral rope effect or concentration of the fuel which is formed along the inner surface of the burner nozzle is broken up and dis persed so. that a uniform distribution of fuel is had about the entirecircumference of the burner nozzle as the fuel is discharged therefrom.

Another object is torelieve the low pressure zone cre ated at the center of the nozzle to prevent the occurrence of back-flow of fuel and air thereat.

And still another object of this invention is to introduce the secondary air in a manner whereby it is uniformly delivered over the entire area of the burner throat or opening so as to thoroughly and completely mix with the fuel entering a furnace.

The foregoing objectsand advantages of this invention are attained by a pulverized fuel burner comprising essentially of a tubular nozzle having an inlet and discharge end, means in communication with the inlet of the nozzle and forming a volute chamber for receiving and spirally flowing a mixture of pulverized fuel and carrier air axially along the nozzle whereby the pulverized fuel tends to concentrate in a spiral rope fashion along the inner surface thereof, a plurality of helical ribs twisted in a direction counter to the rotation or spiral of the rope formation on the inner surface of the nozzle for dispersing the rope effect, means for relieving the low pressure area created by the whirling mass of fuel and air within the nozzle to prevent a backflow thereat and means for introducing secondary air adjacent the discharge end of the nozzle whereby the latter is effectively distributed across the entire area of a burner opening in a furnace 'wall asso.- ciated therewith.

A feature of this invention resides in the provision of helical ribs disposed on the inner surface of the burner nozzle and twisted in a direction opposite or counter to the whirling movement of the fuel and air stream flowing axially thereto.

Another feature resides in the provision of an inner nozzle having an inlet end portion in communication with said volute chamber and through which a portion of the fuel and air mixture flows to relieve the low pressure area created by the whirling mixture flowing axially thereof.

Another feature resides in the provision of a secondary air means having a duct concentrically disposed about the discharge end of the nozzle for dividing the secondary air into an inner and outer band to distribute the air more effectively over the entire area of the burner openmg.

Still another feature resides in the use of skimmer vanes disposed within the volute chamber for dividing the fuel and carrier air mixture into a plurality of streams and thereby assisting the ribs in discharging the fuel and air mixture uniformly about the entire circumference of the nozzle upon discharge therefrom.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described preferred embodiments of the invention.

In the drawings:

FIG. 1 is a side view of a pulverized fuel burner in accordance with this invention having portions thereof broken away and. shown in section.

PEG. 2 is the sectional view taken along line 22 of FIG. 1, having portions thereof broken away.

FIG. 3 is an enlarged detailsectionalside view of the outer nozzle.

FIG. 4 is an end view of FIG. 3.

Referring to FIG. 1, the burner 10 of the instant invention, designed to burn a pulverized fuel, such as coal and the like, is illustrated in association with a. furnace wall 11-. A burner opening in wall 11 is defined by frustoconical burner throat 12, As shown, the inner surface of the throat diverges toward the furnace side of the wall and is cooled by fluid cooled tubes 13.

Spaced from the furnace wall 11 is an outer burner wall 14- which defines therebetween an air plenum chamber 1-5 in which combustion air from an air blower (not shown) is delivered to a burner windbox 16 located within the air plenum chamber 15. A damper 17 operated by a suitable operating means 18 controls the amount of air entering the windbox.

Located in the burner wall 14 in axial alignment with the burner throat 12 is a circular access opening 19. Ac.- cording to this invention the burner it} includes a cylinr drical nozzle 20 which extends through the access opening closure 21, across the air chamber 15 and windbox 16 to a point adjacent to the burner throat 12. Connected to the inlet end 263A of the nozzle is a means forming a volute chamber 22. As shown the volute chamber 22 is bounded by a pair of side walls 23-, 24 spaced apart by a transversely extending curvilinear plate 25 defining a scroll.

Air-borne pulverized fuel is delivered to the scroll or volute chamber 22 through an inlet duct 26 entering substantially tangential of chamber 22. The fuel is discharged therefrom through an axial opening 27 which is in communication with the inlet end 29A of the nozzle 29. The fuel and carrier air thus delivered to the volute chamber 22 has imparted thereto a whirling or spinning movement as the fuel-air mixture flows from the tangential inlet to the axial outlet of the volute chamber. in doing so the fuel and air mixture continues to whirl as it flows axially through nozzle 20. As the fuel and air is Whirled through the nozzle the heavier solid particles of fuel tend to form a spiral rope, and at the center of the whirling mass of fuel and air there is created a low pressure zone.

Because of the spiral rope effect the fuel is not uniformly distributed about the entire circumference of the nozzle. When this occurs, the flame conditions within the furnace maybe such as to cause an exceptionally heavy flame in one sector of the furnace While one or more or" the other furnace sectors may have an insufficient supply of the fuel, in comparison with the combustion air supplied. Under these conditions, incomplete combustion and high carbon loss can occur.

To assist in distributing the fuel and air about the circumference of the nozzle 20, skimmer vanes 28 are disposed in the volute chamber to divide the fuel and air mixture into a plurality of streams. As shown two such vanes are illustrated. These divide the fuel and air mixture into three co-axial, concentric, spiral or Whirling fuel-air streams, the fuel concentrations of which are angularly displaced about the circumference of the nozzle. If desired the skimmer may be rendered adjustable as disclosed in a copending application S.N. 589,546, filed June 5, 1956, now Patent No. 2,921,542.

According to this invention a plurality of spaced, longitudinal, inwardly extending ribs or interrupters 29 are disposed on the interior surface of the nozzle 2t) to disperse or break-up the angularly displaced concentrations of the plural fuel streams to insure an ultimate uniform distribution of the fuel and air about the entire circumference of the nozzle discharge end 2%. As shown, the ribs 29 are equidistantly spaced about the inner wall of the nozzle 20 and are ten in number. The number of ribs, however, may vary depending upon the size and diameter of a particular burner nozzle.

An important feature of this invention is that the ribs 29 are rotated or twisted on the inner surface of the nozzle in a helical direction which is counter to the spin ning of the fuel and air streams flowing therethrough. The reverse or counter spiral twist of the ribs 29 relative to the spiral flow of the fuel air streams through the nozzle is utilized to effect a large angle of intersection between the fuel-air streams and the ribs. Thus as the fuel-air streams are whirling in a direction counter to that of the ribs, the fuel particles in each stream, tending to concentrate along the inner surface of the nozzle, impinge upon the rib at an angle which breaks up the rope or concentration of fuel tending to hug the inner surface of the nozzle and cause some of the larger fuel particles to be projected radially inwardly. As a result the fuel particles are uniformly distributed about the entire periphery of the nozzle. It has been noted by experiment that ribs 29 twisted counter to the whirl of the fuel-air stream are more efiective than straight axially extending ribs in breaking up the fuel concentrations. Counter-twisting the ribs also permits the use of ribs having a smaller cross-sectional area which is important from a pressure drop standpoint.

It was further determined by experiment that if the ribs are twisted A3 of a turn, i.e. traverse a 45 sector of the nozzle circumference over the length of the rib and counter to the flow of the fuel-air streams, satisfactory distribution as well as pressure drop is attained thereby.

As best shown in FIGS. 3 and 4, the ribs 29 are illustrated as rectangular in cross-section. Also that the longitudinal extent of the ribs along the inner surface of the nozzle equals approximately three or four times the inside diameter of the nozzle, and that optimum distribution is obtained when the ends of the ribs terminate slightly inwardly of the discharge end 2013 of the nozzle.

In order to prevent backflow of the fuel and air within nozzle 20, an inner nozzle 30 is concentrically disposed therein and forms therewith an annular chamber 31 through which the main fuel and air streams flow. Referring to FIG. 2 it will be noted that the inner nozzle 36* has a flared or bell shaped, inlet end portion 32, which extends through the axial opening 27 and into the volute chamber 22. With this arrangement a small portion of the fuel and air mixture within the volute chamber 22 is permitted to flow axially through the inner nozzle 30. Thus the pressure within the inner and outer nozzles tends to be equalized thereby relieving any low pressure area which would otherwise be created at the center portion of the whirling mass of fuelair mixture.

To streamline the flow of the fuel-air mixture and minimize the probability of eddies at the inlet end 32 of the inner nozzle 39, a conical shaped member 33 with its apex portion extending toward the inlet 32 is disposed co-axialiy therewith to form an annular inlet chamber 34.

Secondary air is supplied to the burner 10 through an air register means 35 disposed adjacent to the burner throat 12 and about the discharge end 20B of the burner nozzle 26. As shown, the air register 35 comprises a pair of spaced annular members 36 and 37 which form the end walls thereof. The end wall 37 adjacent the burner port has a laterally extending portion 38 converging toward the burner port to define an opening 39 for the discharge of secondary air therefrom.

Circumferentially spaced and pivotally connected between and adjacent the outer periphery of the end walls 36, 37 of the air register are a plurality of register doors 40 adapted to pivot between open and closed position. With the air doors 40 in the open position the air register .35 is rendered in communication with the windbox 16. If desired the air doors 40 may be suitably geared, linked or otherwise connected together so as to be responsive to an operating means 41 which may be either manually or automatically controlled to operate the same. In the illustrated embodiment the operating means 41 comprise a manually operated handle suitably geared to the air doors 40. Thus, in the event that it becomes necessary to shut off the burner, all the doors may be simultaneously moved to a close by the operation of means 41 to cut ofi the air supply to the burner. It will be noted also that the air doors in addition to admitting air into the air register 35 in the open position thereof also imparts to the air entering thereinto a whirling or spinning movement as it exits therefrom through the axial opening 39.

Because of the spin imparted to the secondary air, a relatively large portion thereof is concentrated in a relatively narrow band which tends to hug the inner periphery of the throat 12. As a result very little air is directed to- .ward the inner area of the throat 12.

According to this invention a center duct or sleeve 42 is disposed within the air register 35 and about the discharge end of the nozzle 20 to distribute the air and utilize more effectively the entire area of the throat opening. With this arrangement the secondary air is divided into an inner and outer band of whirling air in which the center duct or sleeve 42 is arranged to confine approximately 25% of the combustion air and cause that portion of the air to be discharged immediately adjacent the fuel nozzle. With this arrangement more of the air is allowed to be thoroughly and uniformly mixed with more of the fuel entering the furnace. Thus optimum combustion conditions are attained resulting in efficient and complete combustion of the fuel.

As shown, the burner herein described may be used separately or in combination with either liquid and/0r gaseous fuel. For this purpose a liquid fuel assembly 43 may be inserted through the end wall 23of the volute chamber 22 to extend through the inner nozzle 30 toward the burner opening with its atomizing tip 44 terminating adjacent the discharge end of the nozzles.

A gaseous fuel is burned through the medium of a gas ring 45 positioned adjacent the burner throat 12 and about the axial opening 39 of the air register. Gaseous fuel is supplied thereto through a supply pipe 46 which connects to a suitable source of supply not shown. Completing the burner assembly as illustrated is an ignitor means 47 and a sighting means 48 While the instant invention has been disclosed with reference to a particular embodiment thereof, it is to be appreciated that the invention is not to be taken as limited to all of the details thereof as modifications and variations thereof may be made without departing from the spirit or scope of the invention.

What is claimed is:

l. A pulverized fuel burner comprising spaced outer and inner tubular nozzles, each of said nozzles having an inlet and discharge end, means in communication with the inlet ends of said nozzles for receiving a mixture of pulverized fuel and carrier air whereby a major portion of said mixture is whirled axially of said outer nozzle so that the pulverized fuel tends to concentrate along the inner surface of said outer nozzle, and a minor portion of said mixture being directed axially through said inner nozzle to relieve the low pressure created by the whirling mass of said major portion of said mixture flowing through said outer nozzle, a plurality of longitudinally extending helical ribs disposed on the inner surface of said outer nozzle to interrupt the flow of spiralling fuel n therethrough at a predetermined angle, said ribs being twisted in a direction counter to the spiralling movement of said mixture to enhance the angle of interruption formed between said ribs and said spiralling fuel flow for dispersing the fuel tending to concentrate along the inner surface of said outer nozzle to enhance uniform distribution of the pulverized fuel about the nozzle dis charge opening formed by the discharge ends of said nozzles, and means provided adjacent to and co-axially with the inlet end of said inner nozzle for enhancing the entrance of said mixture thereinto, said entrance enhancing means comprises a conical member having the apex thereof extending toward the inlet end of said inner nozzle.

2. The invention as defined in claim 1 wherein said inlet end of said inner nozzle is flared outwardly to form with said conical member an annular entrance chamber to said inner nozzle.

3. In combination with a furnace wall having a burner port extending 'therethrough, a pulverized fuel burner comprising means forming a volute chamber having a tangential inlet for receiving a mixture of pulverized fuel and carrier air, and an axial outletin axial alignment with and spaced from said burner port, skimmer means disposed in said volute chaniber'to divide said mixture with a plurality of fuel and air streams, said volute chamber imparting a whirling movement to said streams as the same flow from saidtangential inlet to said axial outlet, an outer tubular nozzle having an inlet and discharge end portion, said inlet end portion being in communication with said axial outlet and said. discharge end portion terminating adjacent said. port, an inner tubular nozzle disposed within said outer nozzleland. forms therewith'an annular chamber, said inner nozzle having an outwardly flared inlet end portion extending axially into said volute chamber and having an outlet end portion terminating adjacent said port whereby a portion of each fuel and air stream discharging from said volute chamber is whirled in an axial direction through said annular chamber with the pulverized fuel tending to concentrate along the inner surface of said outer nozzle and another portion of each fuel and air stream flows axially through said inner nozzle to relieve the low pressure created by the mixture whirling through said annular chamber, means adjacent to and coaxial with the inlet end of said inner nozzle for enhancing the entrance of fuel and air thereinto, said latter means including a conical member having the apex thereof extending toward said flared inlet end of said inner nozzle to form therewith an annular entrance chamber, a plurality of longitudinally extending helical ribs disposed on the inner surface of said outer nozzle to intersect said whirling fuel mixture at a predetermined angle, said ribs being rectangular in cross-section and twisted in a direction counter to the whirling movement of said streams flowing through said annular chamber to increase the angle of intersection therebetween for dispersing the fuel concentration along the inner surface of said outer nozzle so as to provide a uniform distribution of the pulverized fuel about the annular discharge opening formed by said nozzles, said ribs being equidistantly spaced and extended longitudinally of said outer nozzle a distance equal to approximately three times the diameter thereof, and an air register for receiving combustion air disposed about the annular discharge opening formed by said nozzles, said air register having an axial outlet adjacent to and aligned with said burner port, means for imparting a whirling movement to the combustion air flowing through said register, and a duct disposed within said register, said duct being concentrically spaced about the discharge end of said outer nozzle, said duct dividing said combustion air into an inner and outer band of air so that said combustion air is effectively distributed over the entire area of said port.

4. A pulverized fuel burner comprising outer and inner tubular nozzles cooperating to form an annular passage therebetween and each having an inlet and a discharge end, said inner nozzle. extending along substantially the entire length of said outer nozzle and having its discharge end disposed adjacent the discharge end of said outer nozzle; means supplying pulverized fuel to. said nozzles, said last named means including means supplying a portion of the pulverized fuel in a whirling stream of air to the inlet end of said outer nozzle and effecting. a whirling path of travel through said passage. and along said outer nozzle, and means supplying another portion of the pulverized fuel in a stream of air to the inlet end of said inner nozzle for flow therethrough to relieve the. low pressure zone in the center of the whirling stream of fuel and air discharging from said annular passage; and a plurality of longitudinally extending helical ribs dis: posed on the inner surface. of said outer nozzle and twisted in a direction counter to the dire ction of rotation of the whirling stream of fuel and airentering said annular passage, said ribs being so proportioned and; are ranged and twisted as to disrupt and disperse the fuel-0on centrations along the inner surface of said outei' nozzle as said whirling fuel-air stream passes through said an nular passage and yet maintain the original direction of rotation of the whirling fuel-air stream in said passage to provide a substantially uniform circumfer ential distribution of pulverized fuel upon discharge from: saidannular passage.

5. The invention as defined in claim 4 wherein saidribs are of rectangular cross-section. k v

6. The invention as defined in claim 4 wherein said ribs terminate slightly inwardly of the discharge end of said outer nozzle.

7. The invention as defined in claim 6 wherein said outer nozzle is of circular cross-section, and said. ribs are equidistantly spaced and extend along said outer nozzle a distance equal to approximately three times the diameter of said outer nozzle.

8. The invention as defined in claim 7 wherein said ribs make an approximately /8 turn throughout their lengths relative to the circumferenceof said outer nozzle.

9. A pulverized fuel burner comprising outer and inner tubular nozzles cooperating to form an annular passage therebetween and each having an inlet and a discharge end, said inner nozzle extending along substantially the entire length of said outer nozzle and having its discharge end disposed adjacent the discharge end of said outer nozzle; means supplying pulverized fuel to said nozzles, said last named means including means forming a volute chamber opening to the inlet ends of said nozzles, means for introducing a stream of air and pulverized fuel tangentially into said volute chamber and effecting a whirling path of travel therein, means directing a portion of said whirling fuel-air stream to the inlet end of said outer nozzle and effecting a whirling path of travel through said passage and along said outer nozzle, and means directing the remaining portion of said Whirling fuel-air stream to the inlet end of said inner nozzle for flow therethrough to relieve the low pressure zone in the center of the whirling stream of fuel and air dischargnig from said annular passage; and a plurality of longitudinally extending helical ribs disposed on the inner surface of said outer nozzle and twisted in a direction counter to the direction of rotation of the whirling stream of fuel and air entering said annular passage, said ribs being so proportioned and arranged and twisted as to disrupt and disperse the fuel concentrations along the inner surface of said outer nozzle as said whirling fuel-air stream passes through said annular passage and yet maintain the original direction of rotation of the whirling fuel-air stream in said annular passage to provide a substantially uniform circumferential distribution of pulverized fuel upon discharge from said annular passage.

10. A pulverized fuel burner comprising means form ing a volute chamber having a tangential inlet and an axial outlet; outer and inner tubular nozzles cooperating to form an annular passage therehetween opening to the axial outlet of said volute chamber, said outer nozzle having an inlet at one end opening to the axial outlet of the volute chamber and an outlet at its opposite end, said inner nozzle having at one end an outwardly flaring inlet opening to and disposed within said volute chamber and an outlet at its opposite end, said inner nozzle extending along substantially the entire length of said outer nozzle and having its outlet end disposed adjacent the outlet end of said outer nozzle; means supplying pulverized fuel to said nozzles, said last named means including said volute chamber, means for introducing'a stream of air and pulverized fuel into the tangential inlet of said volute chamber and effecting a whirling path of travel in said chamber, and means including said flared inlet end of said inner nozzle for directing a major portion of said whirling fuel-air stream to the inlet end of said outer nozzle and effecting a whirling path of travel through said passage and along said outer nozzle and for directing the remaining portion of said whirling fuel-air stream to the inlet end of said inner nozzle for flow therethrough to relieve the low pressure zone in the center of the whirling stream of fuel and air discharging from said annular passage; and a plurality of longitudinally extending helical ribs disposed on the inner surface of said outer nozzle and twisted in a direction counter to the direction of rotation of the whirling stream of fuel and air entering said annular passage, said ribs being so proportioned and arranged and twisted as to disrupt and disperse the fuel concentrations along the inner surface of said outer nozzle as the whirling fuel-air stream passes through said annular passage and yet maintain the original direction of rotation of the whirling fuel-air stream in said annular passage to provide a substantially uniform circumferential distribution of pulverized fuel upon discharge from said annular passage.

11. In combination with a furnace wall formed with a circular burner port extending therethrough; a pulverized fuel burner comprising means forming a volute chamber having a tangential inlet and an axial outlet; outer and inner tubular nozzles cooperating to form an annular passage therebetween opening to the axial outlet of said volute chamber, said outer nozzle having an inlet at one end opening to the axial outlet of the volute chamber and an outlet at its opposite end concentrically opening to said burner port, said inner nozzle having at one end an outwardly flaring inlet opening to and disposed within said volute chamber and an outlet at its opposite end, concentrically opening to said burner port, said inner nozzle extending along substantially the entire length of said outer nozzle and having its outlet end disposed adjacent the outlet end of said outer nozzle; means supplying pulverized fuel to said nozzles, said last named means including said volute chamber, means for introducing a stream of air and pulverized fuel into the tangential inlet of said volute chamber and effecting a whirling path of travel in said chamber, and means including said flared inlet end of said inner nozzle for directing a major portion of said whirling fuel-air stream to the inlet end of said outer nozzle and effecting a whirling path of travel through said passage and along said outer nozzle and for directing the remaining portion of said whirling fuelair stream to the inlet end of said inner nozzle for flow therethrough to relieve the low pressurze zone in the center of the whirling stream of fuel and air discharging from said annular passage; a plurality of longitudinally extending helical ribs disposed on the inner surface of said outer nozzle and twisted in a direction counter to the direction of rotation of the whirling stream of fuel and air entering said annular passage, said ribs being so proportioned and arranged and twisted as to disrupt and disperse the fuel concentrations along the inner surface of said outer nozzle as the whirling fuel-air stream passes through said annular passage and yet maintain the original direction of rotation of the whirling fuel-air stream in said annular passage to provide a substantially uniform circumferential distribution of pulverized fuel upon discharge from said annular passage to said burner port, and means supplying inner and outer whirling bands of secondary air to said burner at a position adjacent the outlet ends of said nozzles, said last named means including a sleeve surrounding and spaced from said outer nozzle and having an outwardly flaring inlet at one end and an outlet at its opposite end disposed in a plane common to the outlet ends of said nozzles and extending normal to the axes of said nozzles.

References Cited in the file of this patent UNITED STATES PATENTS 1,738,176 Dyer Dec. 3, 1929 2,275,394 Hardgrove Mar. 3, 1942 2,284,708 Woolley June 2, 1942 2,325,442 Vroom July 27, 1943 2,485,656 Raskin Oct. 25, 1949 2,912,942 Whitney et al Nov. 17, 1959 FOREIGN PATENTS 311,905 Great Britain 1929 375,767 Great Britain 1932 377,474 Great Britain July 28, 1932 775,730 Great Britain May 29, 1957 30,593 Netherlands Aug. 15, 1933 

4. A PULVERIZED FUEL BURNER COMPRISING OUTER AND INNER TUBULAR NOZZLES COOPERATING TO FORM AN ANNULAR PASSAGE THEREBETWEEN AND EACH HAVING AN INLET AND A DISCHARGE END, SAID INNER NOZZLE EXTENDING ALONG SUBSTANTIALLY THE ENTIRE LENGTH OF SAID OUTER NOZZLE AND HAVING ITS DISCHARGE END DISPOSED ADJACENT THE DISCHARGE END OF SAID OUTER NOZZLE; MEANS SUPPLYING PULVERIZED FUEL TO SAID NOZZLES, SAID LAST NAMED MEANS INCLUDING MEANS SUPPLYING A PORTION OF THE PULVERIZED FUEL IN A WHIRLING STREAM OF AIR TO THE INLET END OF SAID OUTER NOZZLE AND EFFECTING A WHIRLING PATH OF TRAVEL THROUGH SAID PASSAGE AND ALONG SAID OUTER NOZZLE, AND MEANS SUPPLYING ANOTHER PORTION OF THE PULVERIZED FUEL IN A STREAM OF AIR TO THE INLET END OF SAID INNER NOZZLE FOR FLOW THERETHROUGH TO RELIEVE THE LOW PRESSURE ZONE IN THE CENTER OF THE WHIRLING STREAM OF FUEL AND AIR DISCHARGING FROM SAID ANNULAR PASSAGE; AND A PLURALITY OF LONGITUDINALLY EXTENDING HELICAL RIBS DISPOSED ON THE INNER SURFACE OF SAID OUTER NOZZLE AND TWISTED IN A DIRECTION COUNTER TO THE DIRECTION OF ROTATION 